The present invention relates to a circuit configuration for preventing malfunction of a muting amplifier in a semiconductor integrated circuit.
In the conventional circuit, if the input signal is a non-steady state, there may occur an occasion where the potential at the positive input terminal 5 is rendered lower than -Vcc by a differentiator including a capacitor C1 and a resistor R1. At such a time, the potential at the base 10 of the transistor Q5 comes to drop below -Vcc. And particularly when this potential decreases to be lower than (-Vcc-V.sub.BE), it causes conduction of a parasitic n-p-n transistor 12 whose emitter, base and collector are the base 10 of the transistor Q5, the isolation region and the base 11 of the transistor Q1, respectively.
The same phenomenon happens also with respect to a transistor Q3 or Q4 as in the preceding case of the transistor Q1. And upon conduction of the parasitic transistor 12, a base current comes to flow in each of the transistors Q1, Q3 and Q4 to turn on the transistors Q3 and Q4 as a result, hence inducing a disadvantage that the amplifier function is performed despite the application of muting to eventually produce an unrequired output signal.